Bar codes may be attached to or printed on an object and then used to identify the object. Bar codes can be black and white or they can include color. Bar codes can be one dimensional or two dimensional. Bar codes are sometimes referred to as “spatial codes.”
Cameras may be used to read bar codes. A color camera may be used to read color bar codes. Color cameras typically include a large number of photosensors arranged in an array. Color cameras typically include a painted pixel filter, such as the filter mosaic 24 in U.S. Pat. No. 3,971,065, which “includes individual filters (e.g., filter 26) in one-to-one registration with individual sensor elements of the array (e.g., the element 22).” Column 4, lines 54-58. In U.S. Pat. No. 3,971,065, the painted pixel filter is of the “selective transmitting type,” such that each individual filter allows light of a particular range of colors to pass through. The painted pixel filter is typically arranged over the color camera's photosensor array such that each individual photosensor receives one of the color ranges that the painted pixel filter passes.
Painted pixel filters have filters in several colors arranged in a pattern. The color combinations typically provided in commercially available color cameras include RGB (Red, Green, Blue), RGBE (Red, Green, Blue, Emerald), and CYM (Cyan, Magenta, Yellow), among others. The “Bayer pattern” of U.S. Pat. No. 3,971,065 describes an arrangement of RGB filters.
Accurately reading color bar codes with commercially available color cameras is a challenge.